Evolution of Ultrathin CoFe‐Nanomesh for Oxygen Evolution Reaction: From Slit Pores to Ink‐Bottle Pores

Abstract The time‐dependent mechanism underlying the formation of Co 0.8 Fe 0.2 (OH) x ‐t nanomesh (nanomesh having 80 % Co and 20 % Fe, “t” represents materials synthesis time) has been identified towards the development of a highly effective catalyst for the oxygen evolution reaction (OER). Utilizing 2‐ethyl imidazole (2‐HEIM) as an etching reagent and the Ostwald ripening process enabled the evolution of nanomesh formation with a precise pore size of ink‐bottle shape. Characterization techniques, including N 2 ‐adsorption/desorption, and transmission electron microscopy (TEM) analyses, confirmed the evolution of pore structure from layered double hydroxide‐like structure to hierarchical slit‐pores to uniform ink‐bottle pores after 24 h of synthesis with limited pore shrinkage attributable to iron redeposition at the pore entrances. Atomic force microscopy (AFM) showed a gradual reduction in nanomesh thickness with an increase in synthesis time up to 24 h, indicative of successful exfoliation. The best catalyst (Co 0.8 Fe 0.2 (OH) x ‐24 h) was developed after 24 h of synthesis, having 3.8 nm ink‐bottle‐shaped pores on the basal plane of nanosheets with only 3–4 layers. Co 0.8 Fe 0.2 (OH) x ‐24 h nanomesh exhibited the best catalytic performance, characterized by a 330 mV overpotential, a mass activity of 309.1 A/g, and a turnover frequency of 2.28 s −1 . Furthermore, electrochemical impedance spectroscopy indicated a low charge transfer resistance (5.9 Ω) and pseudoresistance (35.3 Ω), highlighting efficient electron transfer at the electrode/electrolyte interface and enhanced oxygen evolution reaction kinetics, respectively. An increased electrochemical surface area (70.74 cm 2 ) and a high roughness factor of approximately 1010 underlined the importance of narrow mesopores in facilitating catalyst‐electrolyte interactions and improving mass transport. The best material demonstrated remarkable stability during 25 h of electrolysis with a high average current density of 14.5 mA/cm 2 . Hence, this research underscores the critical role of pore morphology in nanomeshes for optimizing catalytic performance and providing stability under vigorous gas evolution due to catalysis.